Buffer Interpreter-local std::string lookup; ValuePrinter needs it.

include/cling/Interpreter/LookupHelper.h

@@ -41,6 +41,7 @@ namespace cling {
   private:
     std::unique_ptr<clang::Parser> m_Parser;
     Interpreter* m_Interpreter; // we do not own.
+    const clang::Type* m_StringTy;
   public:
 
     enum DiagSetting {
@@ -221,6 +222,10 @@ namespace cling {
     bool hasFunction(const clang::Decl* scopeDecl, llvm::StringRef funcName,
                      DiagSetting diagOnOff) const;
 
+
+    ///\brief Retrieve the QualType of `std::string`.
+    const clang::Type* getStringType();
+
   };
 
 } // end namespace

lib/Interpreter/LookupHelper.cpp

@@ -38,7 +38,7 @@ namespace cling {
   // pin *tor here so that we can have clang::Parser defined and be able to call
   // the dtor on the OwningPtr
   LookupHelper::LookupHelper(clang::Parser* P, Interpreter* interp)
-    : m_Parser(P), m_Interpreter(interp) {}
+    : m_Parser(P), m_Interpreter(interp), m_StringTy(nullptr) {}
 
   LookupHelper::~LookupHelper() {}
 
@@ -1896,4 +1896,11 @@ namespace cling {
                                      hasFunctionSelector,
                                      diagOnOff);
   }
+
+  const Type* LookupHelper::getStringType() {
+    if (!m_StringTy)
+      m_StringTy = findType("std::string", WithDiagnostics).getTypePtr();
+    return m_StringTy;
+  }
+
 } // end namespace cling